SchOS/include/schboot.h

// SPDX-License-Identifier: Apache-2.0
#pragma once
#ifndef SCHBOOT_H
#define SCHBOOT_H

// The loader/kernel hand-off, in one place.
//
// Included by kernel/arch/x86_64/entry.S and by boot/uefi/main.c, so the two
// cannot disagree about the magic or the layout. Defining it twice is exactly
// how a loader ends up scanning for bytes the kernel never wrote — the first
// attempt here searched for "SCH6" while the assembler had stored 0x53434836,
// which lands in the file as "6HCS".
//
// Keep this header assembler-safe: no typedefs, no structs outside the C
// guard, nothing entry.S cannot preprocess.

// Scanned for in the first 16 KB of the kernel image, 8-byte aligned, exactly
// as the BIOS loader scans for the multiboot magic. Followed by a little-endian
// 64-bit physical address: the kernel's 64-bit entry point.
//
// The values spell "SCH6" "4BOO" when stored little-endian, which is what
// makes them findable by eye in a hex dump of the image.
#define SCH64_MAGIC0 0x36484353   /* "SCH6" */
#define SCH64_MAGIC1 0x4f4f4234   /* "4BOO" */

// ---------------------------------------------------------------------------
// The hand-off block.
//
// One page of low memory that a loader fills in and the kernel reads. Every
// field below was previously #defined in whichever file happened to need it --
// five of them, across two loaders and two kernel files -- which is the same
// hazard as defining the magic twice, only quieter: nothing breaks until one
// copy moves.
//
// 0x30000 is clear of stage2 (loaded at 0x7E00 and well under 0xA000), the
// multiboot kernel-search buffer at 0x10000-0x14000, and the kernel's own load
// address at 0x100000.
//
// Both loaders write it, so a field's meaning must not depend on which one did.
// Where they genuinely differ -- the BIOS path knows what medium it booted
// from, UEFI does not -- the field is defined as "0 when unknown" rather than
// left for the reader to guess.
#define SCHBOOT_BASE          0x30000

// A VBE mode info block, 256 bytes. The UEFI loader fills the same four fields
// out of GOP rather than translating a structure it never saw, so the kernel
// cannot tell which firmware booted it.
#define SCHBOOT_VBE_INFO      (SCHBOOT_BASE + 0x000)
#define SCHBOOT_VBE_STRIDE    (SCHBOOT_VBE_INFO + 16)   /* uint16, bytes/line */
#define SCHBOOT_VBE_WIDTH     (SCHBOOT_VBE_INFO + 18)   /* uint16 */
#define SCHBOOT_VBE_HEIGHT    (SCHBOOT_VBE_INFO + 20)   /* uint16 */
#define SCHBOOT_VBE_BPP       (SCHBOOT_VBE_INFO + 25)   /* uint8  */
#define SCHBOOT_VBE_LFB       (SCHBOOT_VBE_INFO + 40)   /* uint32, physical */

// Non-zero if the loader was asked for a verbose boot.
#define SCHBOOT_VERBOSE_FLAG  (SCHBOOT_BASE + 0x100)

// What the system booted from. SCHBOOT_MEDIA_CD matters because the ISO path
// reads through ATAPI rather than ATA; 0 means "not stated", which is what the
// UEFI loader leaves, since it does not read the kernel through either.
#define SCHBOOT_MEDIA_FLAG    (SCHBOOT_BASE + 0x101)
#define SCHBOOT_MEDIA_CD      1

// Real-mode spelling of the same byte, for cdboot.S which has no 32-bit
// addressing yet. Segment and offset, not a flat address.
#define SCHBOOT_MEDIA_SEG     0x3000
#define SCHBOOT_MEDIA_OFF     0x101

// The E820 memory map: a uint32 count, then that many 24-byte entries. Capped
// at 32 so a pathological firmware cannot run past the buffer; the map ends at
// 0x508, which is what leaves 0x600 free below.
#define SCHBOOT_E820_COUNT    (SCHBOOT_BASE + 0x200)
#define SCHBOOT_E820_MAP      (SCHBOOT_BASE + 0x208)
#define SCHBOOT_E820_MAX      32

// Where the loader leaves the ACPI RSDP, as a little-endian 64-bit physical
// address. Zero means "not provided, go and look for it yourself".
//
// The kernel's own search scans the EBDA and 0xE0000-0x100000, which is a BIOS
// convention. UEFI publishes the RSDP in its configuration table instead and is
// under no obligation to leave a copy anywhere in particular; OVMF does not.
// Without it the kernel finds no MADT, so no IOAPIC, so no interrupt routing --
// the machine boots to a prompt on polled serial output and then ignores every
// key, which looks like a broken console rather than a missing table.
//
#define SCHBOOT_RSDP_ADDR     (SCHBOOT_BASE + 0x600)

#ifndef __ASSEMBLER__

struct sch64_header {
    unsigned int       magic0;    // SCH64_MAGIC0
    unsigned int       magic1;    // SCH64_MAGIC1
    unsigned long long entry;     // physical address, entered in long mode
};

#endif /* !__ASSEMBLER__ */

#endif /* SCHBOOT_H */